A conventional coke oven battery for producing metallurgical coke comprises coking ovens for carbonizing a coal charge, combustion chambers for causing combustion of a fuel gas, regenerators for storing the remaining heat of a combustion waste gas and sole flues for guiding the combustion waste into a stack. The coking ovens and the combustion chambers are alternately arranged on the regenerators and thus form an oven group belonging to a single combustion system. A huge coke oven battery comprises a plurality of oven groups. Each combustion chamber comprises many flues where a fuel gas is burnt. Coke is produced by heating and carbonizing a coal charge in the coking ovens on the both sides of the combustion chamber through oven walls by said combustion. The fuel gas and the air are sent, after being heated in the regenerators, to the combustion chambers and burnt. Combustion waste gases from the flues are discharged from the stack through the sole flues after heating the regenerators. For the purpose of repeating said regeneration and said preheating of the fuel gas and the air at a high efficiency, the flow direction of the combustion waste gases and the flow direction of the fuel gas and the air are switched over into the reverse direction at certain intervals in time.
In said operation of a conventional coke oven battery, the combustion control is the most important factor with a view to manufacturing a coke of a high quality consistently, reducing the heat consumption, keeping the coke oven battery always in a satisfactory state, and carrying on smooth operations of the coke oven battery.
The conventional method for controlling the combustion in a coke oven battery generally comprises the following steps:
A. SETTING TARGET TEMPERATURES OF THE INDIVIDUAL FLUE BOTTOMS CORRESPONDING TO A TARGET NET COKING TIME (A TARGET INTERVAL OF TIME FROM COAL CHARGING TO COKING COMPLETION) GIVEN BY A COKE PRODUCTION SCHEDULE, WITH REFERENCE TO THE PAST RESULTS AND EXPERIENCE;
B. MANUALLY MEASURING THE BOTTOM TEMPERATURE OF MANY FLUES WITH OPTICAL PYROMETERS ABOUT THREE TIMES A DAY, AND NUMERICALLY CONTROLLING THE MEAN VALUE OF SAID MEASURED TEMPERATURES WITH REFERENCE TO SAID TARGET FLUE TEMPERATURE, ABOUT THREE TIMES A DAY;
C. MANUALLY MEASURING, ON THE OTHER HAND, THE NET COKING TIME FOR THE INDIVIDUAL COKING OVENS, AND NUMERICALLY CONTROLLING THE MEAN VALUE WITHIN AN OPERATING SHIFT OF SAID MEASURED VALUES OF TIME WITH REFERENCE TO SAID TARGET NET COKING TIME, ABOUT THREE TIMES A DAY;
D. MANUALLY CORRECTING THE FLOW RATE AND THE CALORIFIC VALUE OF THE FUEL GAS IN RESPONSE TO THE MARKS IN THE NUMERICAL CONTROL APPLIED IN (B) AND (C) ABOVE; AND
E. MANUALLY ADJUSTING THE STACK DRAFT IN RESPONSE TO THE FLOW RATE AND THE CALORIFIC VALUE OF THE FUEL GAS CORRECTED AS MENTIONED IN (D) ABOVE, WITH REFERENCE TO THE PAST RESULTS AND EXPERIENCE, TO ENSURE EFFICIENT AND SUBSTANTIALLY COMPLETE COMBUSTION OF THE FUEL GAS, AND FURTHERMORE, ANALYZING THE COMBUSTION WASTE GASES WITH WASTE GAS ANALYZERS ABOUT ONCE A WEEK TO FURTHER ADJUST MANUALLY THE STACK DRAFT IN RESPONSE TO SAID ANALYSIS VALUES.
The above-mentioned method for controlling the combustion in a coke oven battery has the following problems:
1.The use of measured net coking times and measured flue temperatures of a low accuracy results in the difficulty in applying an appropriate combustion control; and
2. Measured net coking times are directly employed as a factor for controlling the flue temperature. However, because:
i. A coke oven battery shows a delay in thermal response of about 4 to 5 hours; PA1 ii. A measured net coking time is a result of a thermal history over a period of about 18 to 20 hours from coal charging to coking completion for a coking oven; and PA1 iii. A mean measured net coking time is calculated for each of the coking oven for each work shift (at intervals of about eight hours) and is directly employed as a factor for controlling the flue temperature, but said mean value does not always represent net coking times for all the coking ovens;
this method leads to a considerable delay in thermal response of the coke oven battery, and the mutual dependence between the net coking time and the flue temperature results in a low combustion controllability. These facts eventually necessitate dependence on the human control by intuition;
3. In response to fluctuations in and outside the combustion system, such as the manual adjustment of the stack adjusting damper and the waste gas valves of the individual flues, changes in the fuel gas composition, the correction of the flow rate and calorific value of the fuel gas, variations of the atmospheric temperature, and the adjustment of the air damper, no adjustment of stack draft is applied, for keeping an appropriate air/fuel ratio.
4. The temperature of each flue varies with the carbonizing conditions and the carbonizing cycle dependent on the coke discharging pitches for the adjacent coking ovens. The overall mean flue temperature of the entire oven group also fluctuates under the effect of the unevenness of coke discharging pitches (for example, the unevenness of operational cycle between two oven groups, and that in operations caused by operational shutdown for repairing). A compensation and correction to be made in response to these changes are not taken into account in this method.